The spatial structure of genetic and morphometric variation in Corylus avellana (Betulaceae): pattern and scale

Sammanfattning: In the present thesis, I investigated the spatial structure of genetic and morphometric variation in the widespread wind-pollinated shrub Corylus avellana (L.) Betulaceae, hazel, and related the variation to geographic distribution and different spatial scales. The plant material derived from natural populations in Europe, with special emphasis on the Baltic island of Öland, Sweden. Genetic and morphometric data were obtained from presumably neutral or weakly selected characters such as allozymes and leaf shape. The spatial distribution on Öland was examined using colour infrared aerial photographs. The marginal populations displayed less genetic within-population variation than the central, refugial populations, presumably caused by founder effects during immigration after the latest glaciation. On Öland the species was found to occur in all parts of the island, with large regional differences in patterns of fragmentation, isolation and connectivity. Most of the genetic diversity was explained by differences between shrubs within populations or subpopulations. Allozymes and measures of leaf shape provided different, but complementary, views of the structuring of variation within the species, as well as leading to the hypothesis that spatially-varying selection has contributed to population differentiation in leaf shape. Molecular data revealed populations in which two or more stems or shrubs could be assigned to the same genotype, providing support for layering as a potentially important means of clonal reproduction.